In a mobile communication system including cellular phones, a cellular method is generally used in which a base station covers a large area formed by combining plural areas where the base station may transmit and receive (i.e., cells), and a mobile station changes (switches) from a base station to another base station with the movement of the mobile station.
Currently, services have been available that are based on the third generation mobile communication system using the Direct Sequence Code Division Multiple Access (CDMA) scheme. On the other hand, research and development has also been actively carried out for a next-generation mobile communication system that may provide faster communications. In this regard, in the 3rd Generation Partnership Project (3GPP), a Long Term Evolution (LTE) has been studied to start providing services (see, for example, 3GPP TR25.913 V7.3.0) Further, an LTE-advanced which is a developed version of the LTE has also been studied (see, for example, 3GPP TS36.913 V8.0.1, 3GPP TS36.304, V8.5.0, Sec. 5.2.4, and 3GPP TS36.331 V8.8.0, Sec.6.3.1).